Description

Some typical applications where scuffing may occur are gear teeth, piston rings and
cylinder pairs, cams and followers, splines, sleeve bearings, and parts of swash and wobble plate
compressors. Unlike other tribology-related failures, scuffing occurs very fast, without any
warning, and usually leads to the complete destruction of the sliding pair. Practical experience
with steel has helped to outline safe ranges of operation for some components. Very little,
however, is known about aluminum, which is the second most commonly used engineering metal.
The aim of this study is to obtain a better understanding scuffing and seizure of aluminum/steel
contacts.
The research includes an experimental study of scuffing of aluminum/steel contacts under
dry sliding conditions, a study of the physics of the scuffing process, evaluation of various
hypotheses for scuffmg, and modeling of scuffing.
The experiments are conducted in a custom-designed tribometer, which provides accurate
control of the environmental conditions. Special instrumentation, experimental procedures and
software are developed as a part of the experimental program. These provide a reliable
reproduction and identification of scuffing under laboratory conditions. The scuffing
characteristics of five materials are obtained in air and refrigerant (R134a) environments. The
effects of load, sliding velocity, mechanical strength, environmental temperature, specimen
geometry, time, loading history, and type of environment are evaluated.
The mechanisms leading to scuffing are studied by examination of surfaces, subsurfaces
and wear debris of specimens in the process of scuffing. Quantitative measurements of subsurface
plastic strain are also obtained.
The theoretical part of the study includes the development of a finite element model for the
contact of runned-in rough surfaces and several other models for subsurface stresses,
temperatures, and strains. These models provide information about the local conditions in the
subsurface
Based on the experimental observations and the scuffing models a new hypothesis for
scuffing is proposed. According to this hypothesis, scuffing involves initiation of cracks due to
subsurface plastic deformation, propagation of these cracks leading to the removal of the existing
protective surface layers, and finally cold welding due to adhesion between bare metal surfaces.

Issue Date:

1997-08

Publisher:

Air Conditioning and Refrigeration Center. College of Engineering. University of Illinois at Urbana-Champaign.